In plain English
A team can measure many things, but a KPI focuses attention on what matters to a particular goal. It connects a metric to an outcome the team wants to improve. The KPI is the measure; a target states the result the team aims to reach within a chosen period.
Example
An AI startup wants more customers to keep subscribing. It chooses monthly customer retention rate as a KPI and sets a target of at least 95% each month next quarter. A monthly result of 90% would be below that target.